Hydraulic cements having an extended thickening time, methods of making the same, and processes employing the same



2 995 189 HYDRAULIC CEMENTS I IAVING AN EXTENDED THICKENING TLVIE,METHODS OF MAKING THE SAME, AND PROCESSES EMPLOYING THE This inventionrelates to cements having retarded rates topydratiqnpr to tiss.et.suc1 p'yt, d1m nfethod of mzrtag mee slurn'es. The cemeriFWith which theinvention is concerned is preferably a Portland or Portland-type cement.In another aspect it relates to any hydraulic cement composition in adry form, or with added water in an aqueous slurry form, which when inthe form of an aqueous slurry has a retarded initial set or extended orretarded thickening time and/or a reduced water-loss to adjacent porousformations, due to the addition of a minor but effective amount of anadditive consisting of from 25 percent to 75 percent by weight ofcellulosesulfate selected from the group consisting of icidcellulo sesulfateand its salts, the remainder being selected from the groupconsisting of acid carboxymeth l hydroxyethylncellulose EkidKl Qlmana tssalfs'fthis inviition relating first to sat compositions of matter, secsd to processes of compounding said compositions, and

bl'iUbb KU'EKEWUE United States Patent third to processes for using saidcompositions in the arts of cementing wells, sealing porous formationsduring the drilling of wells, cementing casings in the well, squeezecementing, plugging the well or the earth formation adjacent the same,and grouting or sealing crevices, cracks or holes in man-madeformations, such as buildings, foundations, dams, breakwaters orconcrete and masonry structures, in some instances the cracks orfractures already existing before the slurry is pumped into them, and insome cases the pressure of the slurry being pumped into or against thesurface of said formation or structure forming by its pressure thecracks or fractures to be filled. i In another aspect it relates toobtaining substantially as great, and as important, and increase inthickening time o t c cement, 'when employing as said additive acidcarboxymethyl hydroxyethyl cellulqsg m ixed ether and its salts only, orwith the remaining zero to 2 percen't,of said additive being cellulosesulfate, a'sTvill be obvious from Table I in column 8 comparing theimprovement in both these qualities in runs4 and 9 usingcarpqxymethyihydrgxyethyicellulose. mixed ether m atr the blank run 1,as compared to the results ob- .tained with mixtures in runs 2, 3 and5-8.

This application is a copending continuation of my application SerialNo. 294,674 filed June 20, 1952, which was expressly abandoned on March13, 1959, after the present application was filed.

Among the objects of the invention is the provision of a cement having aretarded rate of hldrgtigp or retarded set, as it will behereinaftertermed, particularly at elevated temperaures and/ or at highpressures up to and above 20,000 pounds per square inch, such as areencountered in cementing of deep wells.

One object of the present invention is to provide a suitable hydrauliccement aqueous slurry and suitable processes employing the same, forcementing casing in wells, for squeeze cementing in wells, and forgrouting cracks, fractures or voids, in natural formations, such as inwells, or in man-made formations such as dams, breakwaters, walls andmassive foundations and structures of all types.

Another object of this invention is to provide a dry 2,995,189. PatentedAug. 8, 1961 hydraulic cement powder which is a novel composition ofmatter, and which may be mixed with water to form w an aqueous cementslurry which is a novel composition of matter and which has at least oneof the following useful properties: a relatively retarded time ofinitial set, a relatively extended thickening time during which it ispumpable, and/ or a relatively low water-loss to porous formations withwhich it may come in contact during cementing or grouting operations.

Further objects of the invention reside in the provision of a slurry ofthe above cement, and in a method of making such slurry.

These and further objects of the invention will be more readily apparentin the following description.

In the cementing of oil wells it is customary to mix a hydraulic cement,for example a Portland or Portlandtype cement, with the requisite amountof water to form a pumpable neat slurry, and to pump the mixture intothe well and down the hole into the place where it is desired to have itharden. In present oilwell drilling practice, with wells commonlyranging from 6,000 to 12,000 feet or more in depth, high temperaturesare encountered at the locations which are to be cemented, andrelatively long periods of time are often required to pump the slurryinto place. Furthermore, in the customary practice of pumping the cementslurry down through the casing and either forcing it out the bottom ofthe casing and upward around the outer surface of the casing, or throughperforations in the lower end of the casing into the formation sought tobe sealed, the slurry is required to pass through narrow channels andsmall openings. Successful placement of the slurry, therefore, requiresthat the slurry shall-remain fluid and pumpabl at high temperatures forseveral hours before it begins to harden. However, after the slurry hasbeen pumped into place, it is desirable to have the hydration or setproceed at a rate at which the slurry will attain its final set anddevelop considerable strength within a reasonable time, say within a fewdays.

As pointed out in the preceding paragraph, the most important functionof the hydraulic cement aqueous slurry of the present invention is thatit has awarded time of initial set, and therefore remains pumpable for arelativelydo'rig period of time and a relatively long period of timepasses before it thickens; et it will attain a finalsuigllenqonsiderable strgngthggithin a reaso a length of time so thatthe well-drilling cfiw'fsfiiot'firidilly delayed, but can get back towork and proceed to continue drilling the well bore, or to perforate thecasing and/or cement with the usual gun perforating tools known to theart. All types of acid cellulose sulfate and all salts of all types ofacid cellulose sulfate when combined as a mixture in the ratios of 1:3to 3:1 with al acid carboxymethyl hydroxyethyl cellulosq tpllfldeather,

mitsefiu'iypes of 'ac'fd'carboxymethyl.cellulose hereinafter beingcalled said additive "when desired) have unexpectedly great setretarding and thickening time extending properties in the practice ofthe present invention; and when the acid cellulose sulfate, or salt ofacid cellulose sulfate, is carefully prepared so that a relatively highdegree of sulfate substitution has occurred with relatively low amountsof degradation of the cellulose molecules, a secondary effect isachieved with said additive which, while not as important as the firstmentioned effect of delaying the time of initial set and extending thethickening time of the cement, is also of considerable value incementing oil wells; namely, the aqueous cement slurry containing theminor but effective amount of said additive has a reduced tendency tolose water to porous formations across the surface of which it must passin going to its intended position in the well. Many failures in priorart oil well cementing jobs, which have been ac- EXAMINEI reset creditedto the premature setting of the cement, are thought to be causedactually by the formation dehydrating the cement slurry, therebyrendering the cement immobile before it reaches the desired position. Asthe practice of using scrapers to clean the mud off the well walls toobtain a better cement-formation bond becomes more frequently used, thebetter the formations may absorb water from the cement slurry causing itnot only to plug the annulus between the casing and the wall of thewell, but also to have insufficient water for normal hydration uponsetting, and the greater will become the realization of the need for lowwater-loss cements.

Everything which is said applying to natural formations in wells appliesalso in some degree to man-made formations being grouted, and the wordformation as used herein is regarded as generic to natural earthformations, geological formations, and man-made formations such asstructures.

In the prior art of squeeze cementing in wells and in forcing grout intothe cracks and crevices in fractured foundations or the like, it hasbeen the practice to employ as a breakdown agent water or drilling mud,which is forced ahead of the aqueous hydraulic cement slurry into theformation to split the same and enlarge the fractures or cracks to befilled, because if ordinary hydraulic cement aqueous slurry wereemployed it would ldse water to the formation or foundation so rapidlythat the cement slurry would start to set before much penetration hasbeen efiected. When a relatively low waterloss hydraulic cement aqueousslurry is employed, the amount of breakdown agent can be greatlyreduced, or entirely eliminated, because the low water-loss cement willpenetrate to much greater distances before io'sing sufficient water tobe caused to set by this dehydralion. When squeezecernenting in oilwells is involved. in which it is desired to force a thin disk or layerof these cement slurrics out into a natural earth formation alongpre-existing or pressure made fractures, in order to separate an ,oilsand fro'm some other sand at the general vicinity where the oil wellintersects the same, it is especially advantageous to use a relativelylow water-loss cement slurry as breakdown agent because then less wateris likely to be absorbed by the oil formation where it might cause areduction in the present or future amount of production of oil. Someoil-bearing formations contain bentonitic materials which swell whenthey encounter water, and if excess water is injected into suchformations, the swelling of the bentonitic material may prevent futureproduction of oil.

It is not believed necessary to have a drawing, or to describe minutelythe well known cementing operations disclosed in such patents as US.2,795,507 and 2,795,508.

By hydraulic cement this invention intends to include all mixtures oflime, silica, and alumina, or of lime and magnesia, silica and aluminaand iron oxide (magnesia for example may replace part of the lime, andiron oxide a part of the alumina), as are commonly known as hydrauliccements. Hydraulic cements include hydraulic limes, grappier cements,puzzolan cements, natural cements and Portland cements. Puzzolan cementsinclude slag cements made from slaked lime and granulated blast furnaceslag. Because of its superior strength Portland cement is preferredamong the hydraulic cements, but as the art of cements recognizeshydraulic cements as a definite class, and as results of value may beobtained with said additive with any member of that class, it is desiredto claim all hydraulic cements. In addition to the ordinary constructiongrades of Portland cements or other hydraulic cements, modifiedhydraulic cements and Portland cements designated as high-early strengthcement, heat resistant cement, and slow-setting cement may be used inthe present invention.

In most oil well cementing and grouting operations it is generallydesirable to use neat cement for added strength, but obviously it isalways possible to add to the 4 ,hydraixifceTg emmatpr, and saidadditive any desire amount 0 inert granular filling material or aggregat such as sand, ground limestone, or any of the other wel known inert orevemm'entitious aggregates, as long a simple tests show the amount addeddoes not reduce the compressive strength after final set below thedesired value. bentonite or other clays are often added to hydrauliccement aqueous slurries, as taught by US. Patent 2,041,- 086 of May 19,1936, or iron oxide of barium sulfate is added to make heavy cement. Anyof these aggregates can be added to the aqueous hydraulic cement slurryof the present invention in the usual proportion used in the prior art.

In operations in previously uncased wells it is often desirable to useneat cement in the practice of the present invention, because inertfilling material may automatically become detached from the walls of thewell, and will tend to mix with and dilute the slurry to such an extentthat it is undesirable to add any filling material to the slurry beingforced into the well. It is customary in the prior art when cementing tomake simple tests as to time of set, compressive strength, etc., onsamples of the proposed mix.

The amount of water added to the cement of the present invention is notcritical, it being obvious that sufiicient water should be added to forma pumpable slurry, and that when the slurry becomes pumpable no furtherwater needed be added. One advantage of the slurry of the presentinvention when a relatively less degenerated acid cellulose sulfate orsalt of the same is used it that it is a low water-loss slurry, andtherefore it is not necessary to add much excess water over the amountmaking the slurry pumpable as a reserve for expected losses, whichexcess water might tend to reduce the final compressive strength of thecement.

It has been found that all hydraulic cements, especially Portland andPortland-type cement aqueous slurrics can be retarded in setting time,the time of thickening extended, and in some cases the water-losstendencies retarded, so that they meet all the above requirements forthe satisfactory cementing of deep wells and like operations by theaddition of a minor but effective amount of from Why hydraulic cement ofa mixture 0 om zeropegcent to 75 percent by weight of cellulose sulfateselected from the group consisting of MWdlsgflflthe remainder beingselected from c group consisting of acid carboxymethyl hydroxyethylcellulose mixed ether and its salts, the salts being those of any metal,ammonium or organic base, or other salts, without seriously affectingthe other desirable properties of the cement. It is preferred at presentto use the sodium or potassium salts of the acid cellulose sulfate, andto use the acid carboxymethyl hydroxyethyl cellulose mixed ether, merelybecause these materials are readily available commercially and thereforeare relatively inexpensive; However, good results are obtained using theacid form of either, or both, the cellulose sulfate and thecarboxymethyl hydroxyethy ce u ose mixed. ether, or any alkali metalsalt, such as the sodium, potassium, lithium, rubidium, caesium andother rare alkali metal salts, the other metal salts, such as the heavymetal salts, or the ammonium or organic base salts, all of which arewater-soluble.

Typical organic base salts that can be used are those derived fromammonia such as methyl amine, dimethyl amine and quaternary ammoniumbases; also pyridine, morpholine and the like. In addition the alkalineearth metal salts such as the barium, calcium, strontium and magnesium,and the heavy metal salts such as the aluminum, iron, copper, lead,silver, mercury, nickel, and all other salts (which are probablyinsoluble in water but which hydrolyze in the hydraulic cement aqueousslurry which is an aqueous alkaline solution) are just as useful in thisinvention in the aqueous hydraulic cement slurry For example, inplugging porous formations,.

which is quite alkaline. Said additive, whether it is composed of saltsformed in the aqueous hydraulic cement slurry by hydrolysis of somewater-insoluble salt, is valuable in amounts of 5 percent or less, basedon the weight of the dry cement, in retarding the set of aqueoushydraulic cement slurry, especially at the temperature and pressureencountered in cementing a well, and in many instances said additivewill decrease the water loss from said aqueous hydraulic cement slurryto porous formations encountered in the well.

While 0.05 percent to 5 percent of said additive by weight of the dryhydraulic cement will give valuable results, it has been found that from0.2 to 1 percent is the most preferred range in wells less ilian 14,000feet deep and less than 300 F., the use of 0.5 percent beingparticularly effective in such wells, and the percentage above 1 whereinS is sulfur, and O is oxygen.

It will be seen that the reaction product of cellulose and sulfuric acidor chlorosulfonic acid contains the sulfate linkage:

wherein OH x ou is an anhydroglucose unit of the cellulose molecule andn is the number of such units in such cellulose molecule, the formulashowing mono-substitution in each unit, whereas in actual practice someunits have double or triple substitution and many units have nosubstitution at all, the degree of substitution merely being an averagevalue.

Cellulose acid sulfate and its salts may be prepared by a number ofsulfating methods old in the prior art, employing either sulfur trioxidegas and the cellulose alone, or sulfuric acid and/or sulfur trioxidealong with various diluents to retard the reaction making it a sulfationreaction with the cellulose, and preventing oxidation; and no matter howthe acid cellulose sulfate is made, it and any of its salts will act toretard the set of a hydraulic cement aqueous slurry and to increase thetimebefore the cement thickens to the point where it is not pumpable.While not to be considered as limits, a relatively high degree ofsulfate substitution for the present invention is about 0.2 or more outof the 3.0 possible in each anhydroglucose unit in the cellulosemolecule (which unit has 3 hydroxyl groups which can be substituted),0.2 being an average, as in an individual anhydroglucose unit the degreeof substitution must always be an integer (1, 2 or 3) or zero. While itis preferred to use an average of between 0.2 and 3 sulfate radicals peranhydroglucose unit, valuable results are obtained outside of thisrange, especially if the cellulose sulfate is water-soluble or willhydrolyze to give water-soluble salts.

The acid cellulose sulfate or salts thereof may be prepared by any oneof several methods as described above, but some of the preferred methodsare those set forth in the Belgian Patent 448,249 of June 30, 1943, ofG. Frank and his u.s. Patent 2,559,914 of July 10, 1951, and US. Patent2,539,541 of January 30, 1951, of G. Malm. Another preferred method isthe reaction of cellulose with a complex of sulfur trioxide, forexample, pyridine-sulfur trioxide, in the presence of a tertiary amine,such as pyridine, and an inert diluent to form the desired product. Thespecific details of the process described in the last sentence areoutlined in a prior copending application Serial No. 133,467 of R. V.Jones filed December 16, 1949 (now Patent 2,697,093), in which saidprocess of preparing acid cellulose sulfate and its salts is claimed.The acid cellulose sulfate may also be prepared by the reaction ofcellulose with an alkali metal chloro-sulfonate under anhydrousconditions, and in the presence of an inert diluent such as benzene, anda tertiary amine. The specific details of this process are outlined in aprior copending application Serial No. 105,452 filed July 18, 1949, ofR. V. Jones (now Patent 2,686,779), in which this process of producingacid cellulose sulfate and its salts is claimed. Still other methods ofpreparing acid cellulose sulfate and salts of the same include thereaction of cellulose with chlorosulfonic acid in the presence of aninert diluent and tertiary amine.

Acid carboxymethyl hydroxyethyl cellulose mixed ether may be made fromcellulose by reacting to form the carboxymethyl portion first and thenthe hydroxyethyl portion, or vice versa, or both at once. Reactingethylene oxide with alkali cellulose is the commercial way to makehydroxyethylcellulose, see page 422 of the book Cellulose Chemistry byHeuser (1946) (John Wiley & Sons, Inc., New York). The reaction is thatof addition and is formulated as:

Sodium Water Ethylene cellulose oxide CsHo05(CHzCHzOH) NaOHHydroxyethylcellulose Sodium hydroxide Other methods are mentioned onpage 423 of said book. C H 0 is one anhydroglucose unit of which thereare many in each cellulose molecule.

' On pages 421 and 422 of said book the preparation ofcarboxymethylcellulose (also known as glycolic acid ether of cellulose)is disclosed. It is formulated as:

CsHeO Na NaOH ClCHrCOOH Sodium Sodium cellulose hydroxideMonochloroacetic NaCl-l- CQHQOrOCHZCOONS H20 Salt Sodium Watercarboxymethylcellulosc By reacting some of the cellulose hydroxyl groupsin a sodium cellulose molecule with ethylene oxide and some with sodiumhydroxide and monochloroacetic acid, sodium carboxymethyl hydroxyethylcellulose mixed ether is formed. This may be converted to acidcarboxymethyl hydroxyethyl cellulose mixed ether by reaction with anacid such as nitric acid and removal of the resulting sodium nitrate orother salt by purification, if purifica tion is desired. When used incement in the present invention, such p 'fication is not alwa snecessary. The substitution of We: be on the same anhydroglucose unit ofthe molecule; sometimes it is, and sometimes not. Nor is it necessarythat all anhydroglucose units be reacted with either, as those units inthe molecule that are so reacted will make the molecule active as acement additive. It is preferred to have a combined substitution ofcarboxymethyl and hydroxyethyl radicals per anhydroglucose unitaveraging from 0.2 to 2.2 in which the carboxymethyl radicals averagefrom 0.15 to 2.15 and the hydroxyethyl'radicals average from 0.05 to2.05 but valuable results are still obtained outside of this range,especially if the mixed ether is watersoluble, or will hydrolyze to givewater-soluble salts.

Portland cement is a mixture of complex silicates and aluminates ofcalcium containing excess lime. The setting or hardening is a result ofthe hydration or other chemical readjustments of the various components.Gencrally speaking, three periods in the set are recognized: initial,final and hardening sets. The initial set normally occurs at ordinarytemperatures in from one to two hours after the mixing, the final settwo to five hours later and the hardening continues for an indefinitetime but it is substantially complete in about 30 days.

The initial set is said to have occurred when a cement slurry has lostits plasticity to such a degree that the two pieces of a broken specimenwill not unite to form a homogeneous mass when placed in close contact.The individual grains of a'cement slurry must remain undisturbed inintimate contact with each other for a time before the initial setoccurs in order to produce a coherent mass. Agitation during the latterpart of the period of initial set will prevent the cement from hardeningproperly to the desired homogeneous, coherent mass.

In order to form a perfect seal in cementing wells, it is necessary thatthe cement be placed before the initial set occurs and it is desirablethat it be placed and allowed to stand for a short period before theinitial set begins. With the equipment available, there is a limit tothe time in which it is possible to mix a cement and pump it into thebottom of the well and up around the casing to the location desired.

Another reason it is necessary to have the cement in place before theinitial set begins is that the viscosity rises as the settingprogresses. This increases the difficulty of pumping and is undesirablebecause of the added strain on the pumping equipment.

is possible to retard the rate of set, within narrow iiinits, byincreasing the alumina content of the cement, but this method is notwidely used because of the high at elevated temperatures as well trnosperic temperatures, ecause obviously a set retarding agent operative atatmospheric temperatures will also retard the set at highertemperatures.

While it is not desired to limit the present invention by any theory ofoperation and while the scope and validity of the claims do not dependupon the validity of any theory of operation, it is believed helpful inunderstanding the invention to think of swan-1ygsorhing-swuchwfqhe-water, the ortlandmement is only slowlyjlhleioobtain enough water tomake its'initial s't, whereby the initial set ofthe cement is greatly retarded. Finally the Portland cement particlestakethe water away from said additive and attain an initial and then afinal set with suitable strength in the cement for use in oil wellcementing operations.

An aqueous slurry of 40 percent water by weight of the dry cement wasmade with Portland cement. This slurry was subdivided into a portion foreach of the following experiments; Said additive was added in theproportions and amounts indicated to all but the first experiment whichacted as a comparison, and the results were recorded in Table I below.The Halliburton thickening time in hours at 180 F.. and the initialwaterloss and water-loss after 1, 2, and 3 hours (in some cases) at 180F., of these tests is recorded.

Table I Additives l Water-Loss, Milliliters/Minutes Run Thic No. eningCel.SO CMHEC, Total. Time, Initial 1 hr. 2 hrs. 3 hrs.

Percent Percent Percent (hours) 0 0 0. 9 0. 7 D 0. 7 36. 8 0. 35 0. 350. 7 58. B 0 0. 7 0. 7 49. 3 0. 0 0. 5 7. 3 0. 375 0. I 0. 5 40. 1 0. 250. 25 0. 5 37. 2 0.125 0. 375 0. 5 24. 8 0 0. 5 0. 5 22. 3

results because the cement. hydrolyzes the same.

The percentage is by weight of the dry Portland cement, which could beany other hydraulic cement with similar results except for compressivestrength which is highest with Portland cement.

2 Obviously, after it set there was no water loss.

cost of high alumina cements and the limited effective range. The rateof set can be retarded also by increasing the amount of water present inthe mix. However, above about to percent water, based on the weight ofdry cement, increased amounts of water will result in weaker cement andthere is no way of knowing exactly how much dilution will result fromwater encountered in the well. Addition of small amounts of gypsum orcalcium sulfate will result in the retarded rate of set, but an excesswill increase the rate and may cause the cement to disintegrate or beweakened. It is, therefore, highly desirable that a retarded cement suchas mine be available for cementing work.

The most convenient method of using said additive in cement is to runthe same and the hydraulic cement through a rotary mixer to produceintimate mixing and later add water to form a fiuid slurry. However,said additive may be added directly to the cement and water at the timeof mixing at the well, or said additive may be F It will be noted inTable I that the water loss reduction and increase, in thickening timeis greatest for the 50 percent cellulose sulfate, 50 percentcarboxymethyl hydroxyethyl cellulose mixed ether, total 0.7 percentmixture, of run No. 3. However, it should also be noted that run No. 4with 0.7 percent carboxymethyl hydroxyethyl cellulose mixed ether aloneis better both as to decrease in water-loss and increase in thickeningtime than run No. 2 with 0.7 percent of cellulose sulfate only. Fromthis it appears obvious that mixtures of the two materials containing 0to 25 percent cellulose sulfate are of great value, although not quiteas effective as with 25 to 75 percent cellulose sulfate.

The retarded set, or extended thickening time, was best measured by theHalliburton thickening time by which is meant the time at which thesetting cement slurry reaches a calibrated poises of viscosity, whichviscosity is approaching about the limit in increasing viscosity that isreadily handled by pumps through some thousands of feet of casing andwell bore outside the casing in a well.

Baroid filter presses operated at 100 pounds per square inch were usedto determine the water-losses of cement slurries.

Thickening times of cement slurries were measured at atmosphericpressure with a Halliburton consistometer.

The water-losses of the cement slurries were determined by the procedurespecified for use on drilling fluids by API Code 29 (1942). Thetreatment of the cement slurry preceding the water-loss determinationconsisted of mixing the water and cement for three minutes to form theslurry and then storing the slurry in sealed jars in an oven at 180 F.

Thickening times of cement slurries were measured at atmosphericpressure in a Halliburton consistometer according to the proceduredescribed in API Code 32, section XII, paragraphs 54 and 67 (1947).Throughout this report thickening time refers to a Halliburtonconsistometer (atmospheric pressure) thickening time unless otherwisespecified.

While numerous examples of the invention have been given for purposes ofillustration, the invention is not limited thereto.

Having described my invention, I claim:

1. A hydraulic cement capable of forming a fluid slurry when mixed withwater, said hydraulic cement having an extended thickening time, saidhydraulic cement comprising a hydraulic cement mixed with a minorproportion by weight of the dry cement of a hydraulic cement thickeningtime extending agent consisting of from 25 percent to 75 percent byweight of cellulose sulfate selected from the group consisting of acidcellulose sulfate and its salts, the remainder being selected from thegroup consisting of ac id carb oxymihyl hydroxyethyl cellulose mixedether and its salts.

2. The process of producing a Portland cement aqueous slurry having anextended thickening time which comprises admixing with Portland cement aminor proportion by weight of the dry cement effective to reduce saidwater-loss of said slurry of an additive consisting of from 25 percentto 75 percent by weight of alkali metal cellulose sulfate, the remainderbeing acid carboxymethyl hydroxyethyl cellulose mixed ether and mixingtherewith sufficient water to produce a fluid slurry.

3. A hydraulic cement capable of forming a fluid slurry when mixed with.water, said hydraulic cement having an extended thickening time, saidhydraulic cement comprising a hydraulic cement mixed with 0.05 percentto percent by weight of the dry cement of a hydraulic cement thickeningtime extending agent consisting of from percent to 75 percent by weightof cellulose sulfate selected from the group consisting of acidcellulose sulfate and its salts,the remainder being selected from thegroup consisting of acid carboxymethyl hydroxyethyl cellulose mixed ethe r and its salts.

4. Ahy u re cement slurry having a retarded setting time at temperaturesabove atmospheric, comprising a hydraulic cement,water and a minorproportion by weight of the dry cement of a hydraulic cement thickeningtime extending agent consisting of from 25 percent to 75 percent byweight of cellulose sulfate selected from the group consisting of acidcellulose sulfate and its salts, the remainder being selected from thegroup consisting of acid carboxymethyl hydroxyethyl cellulose mixedether and its salts.

5. A hydraulic cement slurry having a retarded setting time attemperatures above atmospheric, comprising Portland cement, water and aminor proportion by weight of the dry cement of an additive consistingof from 25 percent to 75 percent by weight of sodium cellulose sulfate,the remainder being acid carboxymethyl hydroxyethyl cellulose mixedether.

6. A hydraulic cement capable of forming a fluid slurry when mixed withwater, said hydraulic cement comprising a hydraulic cement mixed withfrom 0.05 percent to 5 percent by weight of the dry cement of anadditive consisting of from 25 percent to 75 percent by weight of alkalimetal cellulose sulfate,'the remainder being acid carboxymethylhydroxyethyl cellulose mixed ether.

7. A hydraulic cement capable of forming a fluid slurry when mixed withwater, said hydraulic cement comprising Portland cement mixed with aminor proportion by weight of the dry cement of an additive consistingof from 25 percent to 75 percent by weight of sodium cellulose sulfate,the remainder being acid carboxymethyl hydroxyethyl cellulose mixedether.

8. A hydraulic cement slurry comprising a hydraulic cement, water, and aminor proportion by weight of the dry cement of an additive consistingof from 25 percent to 75 percent by weight of alkali metal cellulosesulfate, the remainder being acid carboxymethyl hydroxyethyl cellulosemixed ether.

9. A hydraulic cement slurry comprising Portland cemcnt, water, and from0.05 percent to 5 percent by weight of the dry cement of an additiveconsisting of from 25 percent to 75 percent by weight of alkali metalcellulose sulfate, the remainder being acid carboxymethyl hydroxyethylcellulose mixed ether.

10. In the method of cementing a casing in a well which comprisespumping down through the casing and into the annular space between thecasing and the borehole an aqueous hydraulic cement slurry, the step ofadding to the cement slurry a minor amount by weight of the dry cementof a hydraulic cement thickening time extending agent consisting of from25 percent to 75 percent by weight of cellulose sulfate selected fromthe group consisting of acid cellulose sulfate and its salts, therernainder being selected from the group consisting of acidcarboxymethyl hydroxyethyl cellulose mixed ether and its salts.

11. In the method of cementing a casing in a well which comprisespumping down through the casing and into the annular space between thecasing and the borehole an aqueous hydraulic cement slurry, the step ofadding to the cement slurry an agent consisting of from 25 percent to 75percent by weight of cellulose sulfate selected from the groupconsisting of acid cellulose sulfate and its salts, the remainder beingselected from the group consisting of acid carboxymethyl hydroxyethylcellulose mixed ether and its salts in amounts ranging between 0.2percent and 1 percent by weight of the dry cement in the slurry.

12. In the method of cementing a casing in a well whic comprises pumpingdown through the casing and into the annular space between the casingand the borehole an aqueous Portland cement slurry, the step of addingto the cement slurry a minor but effective amount by weight of the drycement of an additive consisting of from 25 percent to 75 percent byweight of sodium cellulose sulfate, the remainder being acidcarboxymethyl hydroxyethyl cellulose mixed ether sufficient to extendthe thickening time of said slurry.

13. In the method of cementing a casing in a well which comprisespumping down through the casing and into the annular space between thecasing and the borehole an aqueous Portland cement slurry, the step ofadding to the cement slurry a minor but effective amount by weight ofthe dry cement of an additive consisting of from 25 percent to 75percent by weight of alkali metal cellulose sulfate, the remainder beingacid carboxymethyl hydroxyethyl cellulose mixed ether sufiicient toextend the thickening time of said slurry.

14. The process of cementing a hole which extends into a formation whichcomprises placing a hydraulic cement aqueous slurry having an extendedthickening time adjacent to said formation by admixing with hydrauliccement from 0.05 percent to 5 percent by weight of the dry cement of anadditive consisting of from 25 percent to 75 percent by weight of alkalimetal cellulose sulfate, the remainder being acid carboxymethylhydroxyethyl cellulose mixed ether, mixing therewith sufiicient water toproduce a fluid slurry and introducing said slurry into said hole intocontact with said formation.

15. The process of producing a hydraulic cement aqueous slurry having anextended time of set which comprises admixing with hydraulic cement from0.05 percent to percent by weight of the dry cement of a hydrauliccement thickening time extending agent consisting of from percent to 75percent by weight of cellulose sulfate selected from the groupconsisting of acid cellulose sulfate and its salts, the remainder beingselected from the group consisting of acid carboxymethyl hydroxyethylcellulose mixed ether and its salts, and mixing therewith sutficientwater to produce a fiuid slurry.

16. The process of producing a Portland cement aqueous slurry having anextended thickening time which comprises admixing with Portland cement aminor proportion by weight of the dry cement effective to reduce saidwater-loss of said slurry of an additive consisting of from 25 percentto 75 percent by weight of sodium cellulose sulfate, the remainder beingacid carboxymethyl hydroxyethyl cellulose mixed ether and mixingtherewith sufficient water to produce a fluid slurry.

17. The process of cementing a hole which extends into a formation whichcomprises placing a hydraulic cement aqueous slurry having an extendedthickening time adjacent to said formation by admixing with hydrauliccement from 0.05 percent to 5 percent by weight of the dry cement of anadditive consisting of from 25 percent to 75 percent by weight of sodiumcellulose sulfate, the remainder being acid carboxymethyl hydroxyethylcellulose 7". .15 ether, mixing therewith sufiicient water to produce:luid slurry and introducing said slurry into said hole into contactwith said formation.

18. The process of cementing a well which extends into a porousformation which comprises placing a Portland cement aqueous slurryhaving a reduced water-loss adjacent to said porous formation byadmixing with Portland cement a minor proportion by weight of the drycement effective to reduce the water-loss of said slurry of a Portlandcement thickening time extending agent consisting of from 25 percent to75 percent by weight of cellulose sulfate selected from the groupconsisting of acid cellulose sulfate and its salts, the remainder beingselected from the group consisting of acid carboxymethyl hydroxyethylcellulose mix ed ether and its salts, mixing therewith sufiicient waterto produce a fluid slurry and introducing said slurry into said wellinto contact with said porous formations- 19. A cement compositionconsisting essentially of a major portion of a dry hydraulic cementmixed with 0.05 to 5 percent of its weight of a cement thickening timeextending and water loss reducing agent selected from the groupconsisting of acid carboxymethyl hydroxyethyl cellulose mixed ether andits salts, in which the total substitution per anhydroglucose unit ofthe cellulose of carboxyalkyl and hydroxyethyl groups is between 0.2 to2.2, the hydroxyethyl substitution is between 0.05 to 2.05, and thecarboxyalkyl substitution is between 0.15 to 2.15.

20. The composition of claim 19 in which the hydraulic cement isPortland cement.

21. A cement composition aqueous slurry consisting essentially of amajor portion of a dry hydraulic cement mixed with 0.05 to 5 percent ofits weight of a cement thickening time extending and water loss reducingagent selected from the group consisting of acid carboxymethylhydroxyethyl cellulose mixed ether and its salts, in which the totalsubstitution per anhydroglucose unit of the cellulose of carboxyalkyland hydroxyethyl groups is between 0.2 to 2.2, the hydroxyethylsubstitution is between 0.05 to 2.05, and the carboxyalkyl substitutionis 12 between 0.15 to 2.15, and suflicient water to produce a pumpableslurry.

22. The composition of claim 21 in which the hydraulic cement isPortland cement.

23. In the method of cementing a casing in a well which comprisespumping a cement composition aqueous slurry comprising hydraulic cementinto the annular space between the casing and the borehole, the step ofadding to the slurry 0.05 to 5 weight percent of the dry weight of thehydraulic cement in said slurry of a cement thickening time extendingand water loss reducing agent selected from the group consisting of acidcarboxymethyl hydroxyethyl cellulose mixed ether and its salts, in whichthe total substitution per anhydroglucose unit of the cellulose ofcarboxyalkyl and hydroxyethyl groups is between 0.2 to 2.2, thehydroxyethyl substitution is between 0.05 to 2.05, and the carboxyalkylsubstitution is between 0.15 to 2.15.

24. A hydraulic cement slurry composition comprising a dry hydrauliccement, suificient water to produce a pumpable slurry, and 0.05 to 5percent of the weight of said dry hydraulic cement of a cementthickening time and water loss reducing agent consisting of from zero to75 percent by weight of cellulose sulfate selected from the groupconsisting of acid cellulose sulfate and its salts, the remainder beingselected from the group consisting of acid carboxymethyl hydroxyethylcellulose mixed ether and its salts, in which the total substitution peranhydroglucose unit of the cellulose of carboxyalkyl and hydroxyethylgroups is between 0.2 to 2.2, the hydroxyethyl substitution is between0.05 to 2.05, and the carboxyalkyl substitution is between 0.15 to 2.15.

25. The composition of claim 24 in which the hydraulic cement isPortland cement.

26. A hydraulic cement composition comprising a major portion of a drycement, and 0.05 to 5 percent of the weight of said dry hydraulic cementof a cement thickening time and water loss reducing agent consisting offrom zero to 75 percent by weight of cellulose sulfate selected from thegroup consisting of acid cellulose sulfate and its salts, the remainderbeing selected from the group consisting of acid carboxymethylhydroxyethyl cellulose mixed ether and its salts, in which the totalsubstitution per anhydroglucose unit of the cellulose of carboxyalkyland hydroxyethyl groups is between 0.2 to 2.2, the hydroxyethylsubstitution is between 0.05 to 2.05, and the carboxyalkyl substitutionis between 0.15 to 2.15.

27. The composition of claim 26 in which the hydraulic cement isPortland cement.

28. A cement composition consisting essentially of a major portion of adry hydraulic cement mixed with 0.05 to 0.7 percent of its weight of acement thickening time extending and water loss reducing agent selectedfrom the group consisting of acid carboxymethy hydroxyethyl cellulosemixed ether and its salts, in which the total substitution peranhydroglucose unit of the cellulose of carboxyalkyl and hydroxyethylgroups is between 0.2 to 2.2, the hydroxyethyl substitution is between0.05 to 2.05, and the carboxyalkyl substitution is between 0.15 to 2.15.

29. The composition of claim 28 in which the hydraulic cement isPortland cement.

30. A cement composition aqueous slurry consisting essentially of amajor portion of a dry hydraulic cement mixed with 0.05 to 0.7 percentof its weight of a cement thickening time extending and water lossreducing agent selected from the group consisting of acid carboxymethylhydroxyethyl cellulose mixed ether and its salts, in which the totalsubstitution per anhydroglucose unit of the cellulose of carboxyalkyland hydroxyethyl groups is between 0.2 to 2.2, the hydroxyethylsubstitution is between 0.05 to 2.05, and the carboxyalkyl substitutionis between 0.15 to 2.15, and sufficient water to produce a pumpableslurry.

31. The composition of claim 30 in which the hydraulic cement isPortland cement.

32. In the method of cementing a casing in a well which comprisespumping a cement composition aqueous slurry comprising hydraulic cementinto the annular space between the casing and the borehole, the step ofadding to the slurry 0.05 to 0.7 weight percent of the dry weight of thehydraulic cement in said slurry of a cement thickening time extendingand water loss reducing agent selected from the group consisting of acidcarboxymethyl hydroxyethyl cellulose mixed ether and its salts, in whichthe total substitution per anhydroglucose unit of the cellulose ofcarboxyalkyl and bydroxyethyl groups is between 0.2 to 2.2, thehydroxyethyl substitution is between 0.05 to 2.05, and the carboxyalkylsubstitution is between 0.15 to 2.15.

33. A hydraulic cement slurry composition comprising a dry hydrauliccement, sufiicient water to produce a pumpable slurry, and 0.05 to 0.7percent of the weight of said dry hydraulic cement of a cementthickening time and water loss reducing agent consisting of from zero to75 percent by weight of cellulose sulfate selected from the groupconsisting of acid cellulose sulfate and its salts, the remainder beingselected from the group consisting of acid carboxymethyl hydroxyethylcellulose mixed ether and its salts, in which the total substitution peranhydroglucose unit of the cellulose of carboxyalkyl andhydroxyethylgroups is between 0.2 to 2.2, the hydroxyethyl substitution is between0.05 to 2.05, and the carboxyalkyl substitution is between 0.15 to 2.15.

34. The composition of claim 33 in which the hydraulic cement isPortland cement.

35. A hydraulic cement composition comprising a major portion of a drycement, and 0.05 to 0.7 percent of the weight of said dry hydrauliccement of a cement thickening time and water loss reducing agentconsisting of from zero to 75 percent by weight of cellulose sulfateselected from the group consisting of acid cellulose sulfate and itssalts, the remainder being selected from the group consisting of acidcarboxymethyl hydroxyethyl cellulose mixed ether and its salts, in whichthe total substitution per anhydroglucose unit of the cellulose ofcarboxyalkyl and hydroxyethyl groups is between 0.2 to 2.2, thehydroxyethyl substitution is between 0.05 to 2.05, and the carboxyalkylsubstitution is between 0.15 to 2.15.

36. The composition of claim 35 in which the hydraulic cement isPortland cement.

37. A cement composition consisting essentially of a major portion of adry hydraulic cement mixed with a small percentage of its weightsutficient to extend the cement thickening time and reduce the waterloss of aqueous slurries of said cement of an agent selected from thegroup consisting of acid carboxymethyl hydroxyethyl cellulose mixedether and its salts, in which the total substitution per anhydroglucoseunit of the cellulose of carboxyalkyl and hydroxyethyl groups is between02 to 2.2, the hydroxyethyl substitution is between 0.05 to 2.05, andthe carboxyalkyl substitution is between 0.15 to 2.15.

38. The composition of claim 37 in which the hydraulic cement isPortland cement.

39. A cement composition aqueous slurry consisting essentially of amajor portion of a dry hydraulic cement mixed with a small percentage ofits weight sufficient to extend the cement thickening time and reducethe water loss of aqueous slurries of said cement of an agent selectedfrom the group consisting of acid carboxymethyl hydroxyethyl cellulosemixed ether and its salts, in which the total substitution peranhydroglucose unit of the cellulose of carboxyalkyl and hydroxyethylgroups is between 0.2 to 2.2, the hydroxyethyl substitution is between0.05 to 2.05, and the carboxyalkyl substitution is between 0.15 to 2.15,and sufficient water to produce a pumpable slurry.

40. The composition of claim 39 in which the hydraulic cement isPortland cement.

41. In the method of cementing a casing in a well which comprisespumping a cement composition aqueous slurry comprising hydraulic cementinto the annular space between the casing and the borehole, the step ofadding to the slurry a small percentage of the dry weight of saidhydraulic cement suflicient to extend the cement thickening time andreduce the water loss of said aqueous slurry of an agent selected fromthe group consisting of acid carboxymethyl hydroxyethyl cellulose mixedether and its salts, in which the total substitution per anhydroglucoseunit of the cellulose of carboxyalkyl and hydroxyethyl groups is between0.2 to 2.2, the hydroxyethyl substitution is between 0.05 to 2.05, andthe carboxyalkyl substitution is between 0.15 to 2.15.

42. A hydraulic cement slurry composition comprising a dry hydrauliccement, suflicient water to produce a pumpable slurry, and a smallpercentage of the dry weight of said hydraulic cement sufiicient toextend the cement thickening time and reduce the water loss of saidslurry of an agent consisting of from zero to percent by weight ofcellulose sulfate selected from the group consisting of acid cellulosesulfate and its salts, the remainder being selected from the groupconsisting of acid carboxymethyl hydroxyethyl cellulose mixed ether andits salts, in which the total substitution per anhydroglucose unit ofthe cellulose of carboxyalkyl and hydroxyethyl groups is between 0.2 to2.2, the hydroxyethyl substitution is between 0.05 to 2.05, and thecarboxyalkyl substitution is between 0.15 to 2.15.

43. The composition of claim 42 in which the hydraulic cement isPortland cement.

44. A hydraulic cement composition comprising a major portion of a drycement, and a small percentage of the weight of said dry cementsuflicient to extend the cement thickening time and reduce the waterloss or! aqueous slurries of said cement of an agent consisting of fromzero to 75 percent by weight of cellulose sulfate selected from thegroup consisting of acid cellulose sulfate and its salts, the remainderbeing selected from the group consisting of acid carboxymethylhydroxyethyl cellulose mixed ether and its salts, in which the totalsubstitution per anhydroglucose unit of the cellulose of carboxyalkyland hydroxyethyl groups is between 0.2 to 2.2, the hydroxyethylsubstitution is between 0.05 to 2.05, and the carboxyalkyl substitutionis between 0.15 to 2.15.

45. The composition of claim 44 in which the hydraulic cement isPortland cement.

References Cited in the file of this patent UNITED STATES PATENTS Re.23,873 Ludwig Sept. 21, 1954 2,042,484 Rubenstein June 2, 1936 2,427,683Ludwig Sept. 23, 1947 2,471,632 Ludwig May 31, 1949 2,514,021 AbrahamJuly 4, 1950 2,539,451 Malm et al. Jan. 30, 1951 2,560,611 Wagner July17, 1951 2,618,595 Gloor Nov. 18, 1952 2,629,667 Kaveler Feb. 24, 1953

1. A HYDRAULIC CEMENT CAPABLE OF FORMING A FLUID SLURRY WHEN MIXED WITHWATER, SAID HYDRAULIC CEMENT HAVING AN EXTENDED THICKENING TIME, SAIDHYDRAULIC CEMENT COMPRISING A HYDRAULIC CEMENT MIXED WITH A MINORPROPORTION BY WEIGHT OF THE DRY CEMENT OF A HYDRAULIC CEMENT THICKENINGTIME EXTENDING AGENT CONSISTING OF FROM 25 PERCENT TO 75 PERCENT BYWEIGHT OF CELLULOSE SULFATE SELECTED FROM THE GROUP CONSISTING OF ACIDCELLULOSE SULFATE AND ITS SALTS, THE REMAINDER BEING SELECTED FROM THEGROUP CONSISTING OF ACID CARBOXYMETHYL HYDROXYETHYL CELLULOSE MIXEDETHER AND ITS SALTS.